Update the handbook for release/3.6.
Compare changes
What this MR does / why does DuMux need it:
Update the current version of DuMux and adapt phrasing.
Notes for the reviewer
We could add another section (section 6.3.4) for the FCDiamond discretization scheme. However, I would suggest to include that until release/3.7 as it will require some team communication.
Before you request a review from someone, make sure to revise the following points:
CHANGELOG.md
.\n
character. Make sure there is no \ No newline at end of file
comment in "Changes" of this MR.